Agitator ball mills are used for the size-reduction and homogenisation of solid particles, wherein auxiliary grinding bodies are moved intensively by means of an agitator shaft. The solid particles are thereby size-reduced by impact, pressure, shearing and friction. In principle, agitator ball mills can be different with regard to a horizontal or vertical orientation of the grinding chamber. The activation of the auxiliary grinding bodies takes place by means of the agitator shaft, which can be provided with agitator elements such as for example rods or discs. The grinding chamber is usually filled up to seventy to ninety percent with auxiliary grinding bodies in the size range from 0.03-9 mm.
The product to be ground flows continuously in the grinding process from a product inlet axially through the grinding chamber to a product outlet. The separation of the auxiliary grinding bodies from the product flow then takes place in an outlet region by means of a separating system.
The throughput and the size of the grinding bodies are limited by the separating device in closed agitator ball mills. With the aid of the separating device, the auxiliary grinding bodies are intended to be reliably held back in the grinding container and, even in the presence of high throughput rates, must not lead to compression of the grinding bodies or to blockages. The separating devices can be constituted in a known manner as splitting systems, centrifugal systems or as external separating systems. Known splitting systems are for example sieve cartridges or split tubes, which can be disposed at different points of the grinding chamber.
Centrifugal systems are also known from the prior art as dynamic separating devices, wherein the auxiliary grinding bodies are accelerated radially, as a result of which the latter are transported back into the grinding container on account of the acting centrifugal force. Such dynamic separating devices can be constituted for example by a cage rotating around a sieve, the use whereof finds particular application in the case of high throughput rates or when use is made of extremely small grinding bodies.
An agitator ball mill is known for example from DE 102007043670 A1, wherein a part of the drive energy is transmitted to auxiliary grinding bodies by means of an agitator shaft connected to a drive, as result of which penetration of the auxiliary grinding bodies into the grinding stock outlet is prevented.
Another agitator ball mill known from the prior art with a grinding body separating system (DD 256460 A1) comprises a separating sieve, with the aid whereof the auxiliary grinding bodies are intended to be held in the grinding chamber. The grinding body separating system is constituted for this purpose by a rectangular, box-type sieve frame, a lower curved separating sieve with a rectangular shape and a grinding body sieve trap lying beneath the latter at a distance. The actual grinding body separation is brought about by the separating sieve constituted rectangular, which is fastened to the sieve frame by means of holding elements on two opposite sides, which is inserted with both sieves as a closed modular unit into the grinding container.
A further agitator ball mill provided with a dynamic separating system is disclosed in European patent application EP 1468739 A1, wherein the separating device is disposed in front of a stock outlet and is constituted by a separating element and a drive element driving the latter. The separating element comprises two circular discs disposed coaxial with the chamber axis, between which discs a plurality of conveying or wing elements are disposed, being distributed symmetrically about the centre-point of the discs and leading inwards from the edge of the disc, said conveying or wing elements generating a counter-pressure on the stock/grinding body mixture during operation of the agitator ball mill, so that the auxiliary grinding bodies are separated from the product and conveyed back into the interior as a result of the centrifugal force and the different specific density.
The separating devices known from the prior art for agitator ball mills are able to prevent auxiliary grinding bodies from passing into the product outlet, but it has been shown in practice that an increased concentration of auxiliary grinding bodies occurs in the region of the separating device. The actual grinding process does not however take place in this region, but in the grinding chamber in a region before the separating device. The low concentration of auxiliary grinding bodies in the region that is particularly effective for grinding causes a reduced grinding efficiency, which can lead to an unsatisfactory grinding result.
It would therefore be desirable to make available an agitator ball mill with a separating system which enables an improved distribution of the auxiliary grinding bodies in the grinding chamber. The desired uniform distribution of the auxiliary grinding bodies in the grinding chamber should be possible without design modifications, additions or conversions of the grinding chamber. The known devices of the aforementioned type, however, are not entirely suitable for a uniform auxiliary grinding body distribution.